JP2004102090A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus which is provided with a high-performance zoom lens system and is nevertheless compact. <P>SOLUTION: The imaging apparatus is provided with the zoom lens system which has a plurality of lens groups and forms the output image of an object in a manner as to continuously and optically vary magnification by changing the spacing between a plurality of the lens groups, and an imager which converts the optical image formed by the zoom lens system into an electric signal. The zoom lens system includes, successively from an object side, the first lens group which has positive power as a whole, the second lens group which is arranged apart the variable air spacing between itself and the first lens group, and has negative power, and a third lens group which is arranged apart the variable air spacing between itself and the second lens group, has positive refracting power as a whole, and includes a reflecting surface to bend a luminous flux approximately 90°. The third group comprises, successively from the object side, the reflecting surface and a lens element of positive power arranged apart the air spacing from the reflecting surface. <P>COPYRIGHT: (C)2004,JPO

Description

図３乃至図４は実施例１〜実施例２の収差図であり、各実施例のズームレンズ系の無限遠合焦状態での収差を表している。図３乃至図４中、（Ｗ）は最短焦点距離状態、（Ｍ）は中間焦点距離状態、（Ｔ）は最長焦点距離状態における諸収差｛左から順に、球面収差等、非点収差、歪曲収差、Ｙ’（ｍｍ）は撮像素子上での最大像高（光軸からの距離に相当）｝を示している。球面収差図において、実線（ｄ）はｄ線に対する球面収差、一点鎖線（ｇ）はｇ線に対する球面収差、二点鎖線（ｃ）はｃ線に対する球面収差、破線（ＳＣ）は正弦条件を表している。非点収差図において、破線（ＤＭ）はメリディオナル面での非点収差、実線（ＤＳ）はサジタル面での非点収差を表している。また、歪曲収差図において、実線はｄ線に対する歪曲％を表している。
【００３８】
【発明の効果】
以上説明したように、各実施形態のズームレンズ系によれば、高性能で高倍率ズームレンズ系を備えながら、コンパクトな、撮像装置を提供することができる。
【図面の簡単な説明】
【図１】第１の実施形態（実施例１）のレンズ構成図。
【図２】第２の実施形態（実施例２）のレンズ構成図。
【図３】実施例１の無限遠合焦状態での収差図。
【図４】実施例２の無限遠合焦状態での収差図。
【図５】実施例１の使用状態を示す構成図。
【図６】本発明の概略を示す構成図。
【符号の説明】
ＬＰＦ：光学的ローパスフィルタに相当する平行平面板
ＳＲ：撮像素子
ＴＬ：ズームレンズ系
Ｇｒ１：第１レンズ群Ｇｒ１
Ｇｒ２：第２レンズ群Ｇｒ２
Ｇｒ３：第３レンズ群Ｇｒ３
ＰＲ：内面反射プリズム
ＳＴ：絞り[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an imaging device that converts an optical image formed on a light receiving surface such as a CCD (Charge Coupled Device) or a CMOS sensor (Complementary Metal-oxide Semiconductor) into an electric signal. The present invention relates to an imaging apparatus provided, and particularly to a digital camera; an imaging apparatus which is a main component of a camera built in or external to a personal computer, a mobile computer, a mobile phone, a personal digital assistant (PDA), or the like. . More specifically, the present invention particularly relates to a small-sized imaging device having a zoom lens system.
[0002]
[Prior art]
2. Description of the Related Art In recent years, digital cameras that convert an optical image into an electric signal using an imaging device such as a CCD or a CMOS sensor instead of a silver halide film, digitize the data, and record or transfer the data have been rapidly spreading. I have. In such digital cameras, recently, CCDs and CMOS sensors having high pixels such as 2 million pixels or 3 million pixels have been provided at relatively low cost, so that high-performance imaging devices equipped with an image sensor have been developed. The demand has been greatly increased, and in particular, a compact image pickup apparatus equipped with a zoom lens system capable of zooming without deteriorating image quality has been desired.
[0003]
Further, in recent years, with the improvement of image processing capability of semiconductor elements and the like, an imaging device has been built in or externally attached to a personal computer, a mobile computer, a mobile phone, a personal digital assistant (PDA), and the like. This has spurred demand for high-performance imaging devices.
[0004]
A zoom lens system used in such an imaging apparatus includes, in order from the object side, a first lens group having a positive power, a second lens group having a negative power, and a subsequent lens group. Many so-called plus-lead zoom lens systems have been proposed. The plus-lead zoom lens system is said to be suitable for rear focus and inner focus systems because it is relatively easy to increase the magnification and the focus group can be formed by a group other than the lens group arranged on the most object side. There are features.
[0005]
On the other hand, as a plus-lead zoom lens system, there is a zoom lens system conventionally proposed as a photographing lens system of a silver halide film camera. However, these zoom lens systems are provided corresponding to each pixel of an image sensor having a particularly high number of pixels, particularly since the exit pupil position of the lens system in the shortest focal length state is relatively close to the image plane. However, there is a problem that the pupil of the microlens does not match and the peripheral light amount cannot be sufficiently secured. In addition, since the exit pupil position fluctuates greatly at the time of zooming, there is also a problem that it is difficult to set the pupil of the micro lens. Further, in the first place, the optical performance such as the required spatial frequency characteristic is completely different between the silver halide film and the image pickup device, so that sufficient optical performance required for the image pickup device cannot be secured. For this reason, it has been necessary to develop a dedicated zoom lens system optimized for an imaging device having an imaging element.
[0006]
On the other hand, in order to reduce the size of the image pickup apparatus, a proposal has been made in which a zoom lens system is bent in the middle of the optical path to achieve compactness without changing the optical path length. For example, Japanese Patent Application Laid-Open No. Hei 10-20191 discloses that, in a third lens group of a plus-lead zoom lens system, a reflecting surface is provided on an optical path and bent by approximately 90 °, and then optically transferred onto an image sensor through a moving lens group. An imaging device that forms an image has been proposed. The imaging device disclosed in the publication discloses a third lens group in which a convex surface of a plano-convex lens is directed toward an object side, and a prism having a reflecting surface on a flat surface side is integrally arranged to form a third lens group. After being bent, it has a configuration that reaches the image sensor through a fourth lens group having a movable positive power.
[0007]
As another example, Japanese Patent Application Laid-Open No. H11-258678 discloses that a reflecting surface is provided on the image side of a fixed meniscus-shaped fixed lens element and a movable positive lens group. , A configuration that leads to an image sensor through a positive lens group is disclosed.
[0008]
[Problems to be solved by the invention]
However, the zoom lens system described in JP-A-10-20191 still has room for improvement to be more compact.
[0009]
On the other hand, JP-A-11-258678 only discloses the configuration of the lens barrel, and has a problem that the specific configuration of the zoom lens system is unknown. In an image pickup apparatus provided with a zoom lens system, it is difficult to achieve overall miniaturization unless the zoom lens system occupying the largest space in volume is optimized.
[0010]
The present invention has been made in view of the above problems, and has as its object to provide a compact imaging device having a high-performance zoom lens system.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, an imaging apparatus according to the present invention has a plurality of lens groups, and continuously changes the optical image of an object optically by changing an interval between the plurality of lens groups. An image pickup apparatus comprising: a zoom lens system capable of being formed; and an image sensor for converting an optical image formed by the zoom lens system into an electric signal, wherein the zoom lens system has a positive power as a whole in order from an object side. A first lens group having a negative power and a second lens group having a negative power and disposed between the first lens group and the first lens group. And a third lens group including a reflecting surface that bends the light flux by approximately 90 °, and the third lens group includes, in order from the object side, Reflective surface and reflective surface A lens element with a positive power arranged through an air gap, in that they are composed of and wherein.
[0012]
Another aspect of the present invention is a digital camera including the imaging device. In the past, the term digital camera used to refer exclusively to those that record optical still images, but those that can simultaneously handle moving pictures and digital video cameras for home use have also been proposed, and at present there is no particular distinction between them. It is getting better. Therefore, hereinafter, the term digital camera refers to a camera mainly including an imaging device including an imaging device that converts an optical image formed on a light receiving surface of an imaging device such as a digital still camera or a digital movie into an electric signal. Shall be included.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0014]
For example, as shown in FIG. 6, an imaging apparatus according to an embodiment of the present invention includes a zoom lens system, a TL, and an optical low-pass filter that form an optical image of an object in a variable size order from the object side (subject side). It comprises an LPF and an image sensor SR that converts an optical image formed by the zoom lens system TL into an electric signal. Further, the zoom lens system includes a first lens group Gr1 having a prism PR having a reflecting surface inside, and a subsequent lens group. The imaging device is a main component of a digital camera; a video camera; a camera built in or external to a personal computer, a mobile computer, a mobile phone, a personal digital assistant (PDA), or the like.
[0015]
The zoom lens system TL includes a plurality of lens groups including a first lens group Gr1, a second lens group Gr2, and a third lens group Gr3, and changes an interval between the lens groups to form an optical image. It is possible to change the size. The first lens group Gr1 has a positive power, the second lens group Gr2 has a negative power, the third lens group Gr3 has a positive power, and the third lens group Gr3 has an optical axis of the object light therein. It has a prism PR that bends at about 90 °.
[0016]
The optical low-pass filter LPF has a specific cutoff frequency for adjusting the spatial frequency characteristics of the taking lens system and eliminating color moiré generated in the image sensor. The optical low-pass filter of the embodiment is a birefringent low-pass filter formed by laminating a birefringent material such as quartz whose crystal axis is adjusted in a predetermined direction, a wave plate that changes the plane of polarization, and the like. Note that, as the optical low-pass filter, a phase-type low-pass filter or the like that achieves the required optical cutoff frequency characteristics by the diffraction effect may be employed.
[0017]
The image sensor SR is composed of a CCD having a plurality of pixels, and converts an optical image formed by the zoom lens system into an electric signal by the CCD. The signal generated by the image sensor SR is subjected to predetermined digital image processing, image compression processing, or the like as necessary, and is recorded as digital video signals in a memory (semiconductor memory, optical disk, or the like). The signal is transmitted to another device through the device or converted into an infrared signal. Note that a CMOS sensor (Complementary Metal-oxide Semiconductor) may be used instead of the CCD.
[0018]
FIGS. 1 and 2 are configuration diagrams showing a lens arrangement in a shortest focal length state of a zoom lens system included in an imaging apparatus according to the first and second embodiments of the present invention. In each of the drawings, the prism PR having an internal reflection surface is represented by a parallel plate, and the optical path is represented linearly.
[0019]
The zoom lens system used in the imaging apparatus according to the first embodiment includes, in order from the object side, a first lens element L1 having a negative meniscus lens shape having a convex surface facing the object side and a positive lens element L2 having a biconvex shape. A first lens group Gr1, a bi-concave third lens element L3, a positive meniscus lens-shaped fourth lens element L4 with the convex surface facing the object side, and a prism PR. The positive meniscus fifth lens element L5 having a convex surface facing the object side, the aperture ST and the object side, the biconvex sixth lens element L6, and the biconcave seventh lens element L7 are joined in this order from the object side. A fourth lens group including a first cemented lens DL1 and an LPF corresponding to an optical low-pass filter. During zooming from the wide-angle end to the telephoto end, the first lens unit Gr1 and the third lens unit Gr3 are fixed with respect to the image sensor, and the second lens unit Gr2 moves monotonously to the image side, and the fourth lens unit Gr. Gr4 once moves toward the object side and then moves toward the image side in a U-shaped trajectory. Note that the image side surface of the third lens element L3 and the image side surface of the seventh lens element L7 are aspherical, respectively. FIG. 5 shows a usage state of the zoom lens system of the imaging apparatus according to the first embodiment at the wide-angle end.
[0020]
The zoom lens system used in the imaging apparatus according to the second embodiment includes a negative meniscus lens-shaped first lens element L1 having a convex surface facing the object side and a biconvex positive lens in order from the object side and sequentially from the object side. A first lens group Gr1 composed of an element L2, a second lens group composed of a biconcave third lens element L3, and a positive meniscus lens-shaped fourth lens element L4 with the convex surface facing the object side. Gr2, a prism PR, an aperture ST, a positive meniscus fifth lens element L5 having a convex surface facing the object side, a biconvex sixth lens element L6, and a biconcave seventh lens element L7 from the object side. It comprises a first cemented lens DL1 joined in this order and an LPF corresponding to an optical low-pass filter. During zooming from the wide-angle end to the telephoto end, the first lens unit Gr1 and the third lens unit Gr3 are fixed with respect to the image sensor, and the second lens unit Gr2 moves monotonously to the image side, and the fourth lens unit Gr. Gr4 once moves toward the object side and then moves toward the image side in a U-shaped trajectory. Note that the image side surface of the third lens element L3, the image side surface of the seventh lens element L7, and the object side surface and the image side surface of the eighth lens element L8 are each aspherical.
[0021]
The zoom lens system according to each embodiment includes a rhythm PR in the third lens group so as to have a reflection surface that bends the optical axis of the object light by approximately 90 °. As described above, by bending the optical axis of the object light by approximately 90 °, it is possible to achieve the apparent reduction in thickness of the imaging device.
[0022]
When taking a digital camera as an example, an image pickup apparatus including a zoom lens system occupies the largest volume in the apparatus. In particular, when digital elements such as a conventional lens shutter type film camera are arranged linearly with optical elements such as lenses and diaphragms included in a zoom lens system without changing the direction of the optical axis, the thickness of the camera becomes large. The size in the direction is practically determined by the size from the configuration closest to the object side of the zoom lens system included in the imaging device to the imaging device. However, with the recent increase in the number of pixels of the image pickup device, the aberration correction level of the image pickup device has been dramatically improved. For this reason, the number of lens elements of the zoom lens system included in the imaging apparatus is also increasing, and it is difficult to achieve a thin shape even when not in use (so-called collapsed state) due to the thickness of the lens elements.
[0023]
On the other hand, by adopting a configuration in which the optical axis of the object light is bent by approximately 90 ° by the reflecting surface as in the zoom lens system of each embodiment, the size of the imaging apparatus in the thickness direction when not in use is closest to the object side. Since it is possible to reduce the size from the lens to the reflection surface, it is possible to achieve an apparently thin imaging device. Further, by adopting a configuration in which the optical axis of the object light is bent by approximately 90 ° by the reflecting surface, the optical paths of the object light can be overlapped in the vicinity of the reflecting surface, so that the space can be used effectively and the imaging device can be used. Can be further miniaturized.
[0024]
The position of the reflecting surface is such that the first lens group Gr1 closest to the object side has positive power, the second lens group Gr2 disposed on the image side of the first lens group Gr1 has negative power, and the third lens group. In a case where Gr3 has a configuration of a zoom lens system having a positive power, it is desirable that the inside of the third lens group Gr3 is provided. In the case of a so-called plus-lead optical system that starts with positive and negative, the stop ST is disposed between the second lens group Gr2 with negative power and the third lens group Gr3 with positive power, so that the light beam is close to the third lens group Gr3. Has converged. Therefore, it is desirable to arrange a reflecting surface in the third lens group Gr3 because the size of the reflecting surface can be minimized.
[0025]
As the reflection surface, any of (a) an internal reflection prism (embodiment), (b) a surface reflection prism, (C) an internal reflection plate mirror, and (d) a surface reflection mirror may be used. An internal reflection prism is optimal. By adopting the internal reflection prism, the object light passes through the medium of the prism, so the surface spacing when transmitting through the prism is more physical than the normal air spacing depending on the refractive index of the medium. The converted surface interval is shorter than the interval. Therefore, when an internal reflection prism is employed as the configuration of the reflection surface, an optically equivalent configuration can be achieved in a more compact space, which is desirable.
[0026]
When the reflecting surface is formed by an internal reflecting prism, the material of the prism desirably satisfies the following conditions.
[0027]
Np ≧ 1.55 (1)
However,
Np is the refractive index of the prism material,
It is.
[0028]
If the refractive index of the prism falls below the above range, the contribution to compactness becomes small, which is not preferable.
[0029]
Furthermore, it is preferable that the thickness be in the following range in addition to the above range.
[0030]
Np ≧ 1.7 (1) ′
Further, the reflecting surface does not have to be a perfect total reflecting surface. The reflectivity of a part of the reflecting surface may be appropriately adjusted so that a part of the object light may be branched, and may be incident on a sensor for photometry or distance measurement. Further, the finder light may be branched by appropriately adjusting the reflectance of the entire reflecting surface.
[0031]
It is preferable that each of the first lens group and the second lens group includes, in order from the object side, two independent lens elements each having a negative power and a lens element having a positive power. In a zoom lens system, since chromatic aberration must be corrected for each lens group, at least one positive lens element and one negative lens element are required. A compact zoom lens system can be achieved by configuring the first lens group Gr1 and the second lens group Gr2 to have a minimum of two positive and negative lenses, respectively. At this time, by arranging the negative lens element and the positive lens element in this order from the object side, the peripheral light flux having a large inclination angle with respect to the optical axis on the wide-angle side is guided to the third lens group Gr3 while relaxing. Therefore, it is possible to satisfactorily correct high-order coma aberration and field curvature.
[0032]
It is desirable that the stop ST be arranged on the image side of the reflection surface in the third lens group Gr3. According to this configuration, a sufficiently converged light beam immediately before the stop is reflected by the reflecting surface, so that the reflecting surface can be made sufficiently small, which is preferable. In particular, when the reflecting surface is formed by an internal reflecting prism, the reduction in the size of the reflecting surface leads to a reduction in the size of the prism.
[0033]
Each lens group constituting each embodiment is constituted only by a refraction lens that deflects an incident light ray by refraction (that is, a lens of a type in which deflection is performed at an interface between media having different refractive indexes). However, it is not limited to this. For example, a diffractive lens that deflects an incident light beam by diffraction, a hybrid refractive / diffractive lens that deflects an incident light beam by a combination of diffraction and refraction, and a refractive index distribution that deflects the incident light beam according to a refractive index distribution in a medium. Each lens group may be constituted by a lens or the like.
[0034]
【Example】
Hereinafter, the configuration and the like of the zoom lens system included in the imaging apparatus embodying the present invention will be described more specifically with reference to construction data, aberration diagrams, and the like. Examples 1 and 2 described here as examples correspond to the above-described first and second embodiments, respectively. The lens configuration diagrams (FIGS. 1 and 2) representing the first and second embodiments are shown in FIGS. And the corresponding lens configurations of Examples 1 and 2 are shown.
[0035]
In the construction data of each embodiment, ri (i = 1, 2, 3,...) Is the radius of curvature (mm) of the i-th surface counted from the object side, and di (i = 1, 2, 3,. ...) indicate the i-th axial top surface interval (mm) counted from the object side, and Ni (i = 1, 2, 3, ...), νi (i = 1, 2, 3, ...). .) Indicate the refractive index (Nd) and Abbe number (νd) of the i-th optical element counted from the object side with respect to the d-line. In the construction data, the axial top surface interval that changes during zooming is a variable interval from the shortest focal length state (wide-angle end, W) to the intermediate focal length state (middle, M) to the longest focal length state (telephoto end, T). Shows the value of The focal length (f, mm) and F number (FNO) of the entire system corresponding to each focal length state (W), (M), (T) are shown together with other data.
[0036]
The surface with * added to the radius of curvature ri indicates a surface constituted by an aspheric surface, and is defined by the following expression (AS) representing the surface shape of the aspheric surface. The aspherical surface data of each example is shown together with other data.
[0037]

3 and 4 are aberration diagrams of the first and second embodiments, and show aberrations of the zoom lens systems of the respective embodiments in an infinity in-focus state. 3 and 4, (W) shows the shortest focal length state, (M) shows the intermediate focal length state, (T) shows various aberrations in the longest focal length state. The aberration, Y ′ (mm), indicates the maximum image height (corresponding to the distance from the optical axis) on the image sensor. In the spherical aberration diagram, the solid line (d) represents the spherical aberration with respect to the d line, the one-dot chain line (g) represents the spherical aberration with respect to the g line, the two-dot chain line (c) represents the spherical aberration with respect to the c line, and the dashed line (SC) represents the sine condition. ing. In the astigmatism diagram, a broken line (DM) indicates astigmatism on the meridional surface, and a solid line (DS) indicates astigmatism on the sagittal surface. Further, in the distortion diagram, the solid line represents the distortion% with respect to the d-line.
[0038]
【The invention's effect】
As described above, according to the zoom lens system of each embodiment, it is possible to provide a compact imaging device while having a high-performance and high-magnification zoom lens system.
[Brief description of the drawings]
FIG. 1 is a lens configuration diagram of a first embodiment (Example 1).
FIG. 2 is a lens configuration diagram of a second embodiment (Example 2).
FIG. 3 is an aberration diagram of Example 1 in a focused state at infinity.
FIG. 4 is an aberration diagram of Example 2 in a state of focusing on infinity.
FIG. 5 is a configuration diagram illustrating a use state of the first embodiment.
FIG. 6 is a configuration diagram showing an outline of the present invention.
[Explanation of symbols]
LPF: Parallel plane plate SR corresponding to an optical low-pass filter: Image sensor TL: Zoom lens system Gr1: First lens group Gr1
Gr2: second lens group Gr2
Gr3: third lens group Gr3
PR: Internal reflection prism ST: Aperture

Claims (5)

A zoom lens system having a plurality of lens groups, wherein the distance between the plurality of lens groups is changed so that an optical image of an object can be continuously and optically variable in magnification; and an optical system formed by the zoom lens system An imaging device including an imaging element that converts an image into an electric signal,
The zoom lens system, in order from the object side,
A first lens group having a positive power as a whole,
A second lens group having a negative power and disposed at a variable air distance from the first lens group;
A third lens group disposed at a variable air distance from the second lens group, having a positive power as a whole, and including a reflecting surface that bends the light beam by approximately 90 °;
The imaging apparatus according to claim 1, wherein each of the first lens group and the second lens group includes, in order from the object side, an independent negative power lens element and a positive power lens element. 2. The imaging device according to claim 1, wherein the stop is arranged on the image side of the reflection surface. The imaging apparatus according to claim 1, wherein the first lens group and the third lens group are fixed to an imaging element during zooming. The imaging device according to claim 1, wherein an optical low-pass filter is arranged between a surface of the zoom lens system closest to the image and the imaging device. A digital camera comprising the imaging device according to claim 1.

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